1. Field of the Invention
This invention relates to a semiconductor device and, in particular, to a semiconductor device including memory cells required to refresh.
2. Description of Related Art
In semiconductor devices such dynamic random access memories (DRAMs), it is necessary to periodically perform refresh operation in order to continuously hold data stored in volatile memory cells. Inasmuch as the refresh operation causes a plurality of sense amplifiers to simultaneously activate, there is a high possibility that the refresh operation makes a unique internal power supply voltage included in the semiconductor device fluctuate as compared with normal access operation. Consequently, Japanese Unexamined Patent Application Publication of Tokkai No. 2003-196977 (which will be also called Patent Document 1), which corresponds to U.S. Patent Application Publication No. 2003/123298 A1, makes a suggestion about a semiconductor memory device wherein it makes a differential amplification time interval of a bit line pair differ between the normal access operation and the refresh operation.
In addition, Japanese Unexamined Patent Application Publication of Tokkai No. Hei 9-213066 (which will be also called Patent Document 2) offers a suggestion concerning a technique using a bank register in order to selectively operate a part of a plurality of banks configuring a memory cell array.
In the manner which is described above, an influence upon the internal power supply voltage differs between the normal access operation and the refresh operation. In a case of performing the refresh operation, the extend of the influence upon the internal power supply voltage differs according to the number of banks which become a subject of refresh and/or according to the number of segments in each bank that become a subject of refresh. When the internal power supply voltage reduces, it has a want of electrical charges for restore on operating the refresh. It results in the creation of problems where it is impossible to perform a sufficient restore with respect to the memory cells which become a subject of refresh.